Went looking for one myself, but the few that were there seemed to be years old, and broken. So I decided to go ahead and whip one up.
http://spiralnine.com/bts/bitcoin.png

As you can see, it's a very bare bones style. (made it to match my other modified illustro gadgets)
It currently supports MtGox, CampBX, BTC-E, and BitStamp. (Will add others if requested)

Color/size can be changed in the Gnometer settings.
Exchanges can be disabled, and currencies changed from within the ini file.


Anyways, If anyone else is interested you can grab it here: ZIP or RMSKIN(deviantart)

Let me know if you use it. Not sure if I was the only one looking. lol


Edit: It's a skin for the Rainmeter.net app if some don't know.

Edit2: Well, I completely redid it to make it look better, and easier to customize. It now requires the Gnometer skin suite for rainmeter.